Method for making polysiloxane resins



Patented Dec. 21, 1948 I UNITED STATES PATE Mn'rnbn roa MAKINGPOLYSILOXANE aasms Charles 0. Doyle. seneiieetady. N. r; mum: to

General Electric Company,

New York a corporation of No Drawing. Application November 21, 1945,

Serial No.

4 claim. (01. ace-46s) The present invention relates to novel polyslloxane resins and to a method of preparing such polysiloxanes. It isparticularly concerned with an improved process of hydrolyzing mixtures.of chlorosilanes having a hydrocarbon-to-silicon ratio greater than 1and less than 1.5 and.ineluding a major portion of methylchlorosilanes.

It is well known that organohalogenosilanes, or mixtures thereof whichmay also contain some silicon tetrahalides, readily hydrolyze when mixedwith water to form silanols which condense or can be caused to condenseto form polysiloxanes. The ease with which the silanols condense isdependent on the nature of the organic radical or radicals. When all orsubstantially all of these radicals are methyl groups the rate ofdehydration or condensation is so rapid that for all practical purposesthe condensation of the silanols occurs simultaneously with thehydrolysis of the chlcrosilanes. Because both reactions occurinstantaneously, the hydrolysis of methylchlorosilanes containinga'sufficient number of chlorine atoms attached to silicon to formheathardenable products by mixing them with water results in theformation of insoluble gels which cannot be used in the manufacture ofuseful resinous compositions or in the formation of products of lowaverage molecular weight rather than the high average molecular weightproducts sought in the preparation of resinous products in general.

Various methods have been devised f,or.controlling the hydrolysisreaction and the earlier attempts along this line had for theirprincipal object the prevention of gel formation during hydrolysis.However, as more and more knowledge accumulated concerning the variousmethods of hydrolysis, it became apparent "that certain methods not onlypermitted the carrying out of the hydrolysis without using iceoricewater mixtures for the more readily hydrolya'abie chlorosilanes butalso resulted in the formation of polysiloxanes having propertiesmarkedly different than those of the earlier known polysiloxanes whichhad the same general formula and were prepared from the samechlorosilane mixtures. It thus appears that the polysiloxanes,particularly those obtained by the cohydrolysis and co-condensation ofmixtures of two or more chlorosilanes, will differ from one another,depending on the conditions of hydrolysis and condensation, in much thesame way that other resinous materials, such as the phenol-formaldehydecondensation products, difier from one another depending upon theconditions under which the resin-forming reactions are caused to takeplace.

One of the earlier methods for controlling the hydrolysis ofmethylchlorosilanes is described in Rochow Patent 2,258,218 andcomprises dissolving the chlorosilane mixture in ether and adding theresultant solution to ice or a mixtureof ice and water. Another processis described and c aimed in the copending application Serial No. 455,617filed August 21, 1942 (now U. 8. Patent 2,398,672, issued April 16,1946) in the name of Robert .O. Sauer and assigned to the same assigneeasthe present invention. The Bauer process comprises the solution of thechlorosllanes in a solvent such as toluene and the addition to thissolution to a mixture comprising water and a higher alcohol such asbutanol. Although the prior methods resulted in the formation of liquid,

heat-hardenable products, they also involved the resinous productscertain disadvantages. Large volumes of solvents were usually necessaryand in some cases possessed poor craze resistance. Certain of themethods did not lend themselves either to the easy separation of thesolvents or the recovery of the hydrogen chloride by-product, both ofwhich are essential in any large scale commercial project.

Another process which was found to produce polysiioxane resins 'ofimproved hardness and stability is described and claimed in thecopending application Serial No. 630,134 filed concurrently herewith inthe name of Harry F. Lamoreaux and assigned to they same assignee as thepresent invention. Briefly described that process comprises the additionof a chlorosilane mixture containing a major. portion ofmethylchlorosilanes to a hydrolysis medium comprising a mixture ofwater, a solvent of the glycol polyether type, such as dioxane,bis-(beta-ethoxyethyl) ether or ethylene glycol diethylether and ahydrocarbon solvent such as mineral spirits having a boiling pointsubstantially above that of the polyether, the hydrolysis being carriedout under gentle reflux temperatures.

The present invention is based on the discovery that the presence ofhigh boiling hydrocarbon, water-immiscible solvent in the hydrolysismedium is not necessary and that polysiloxane resins having improvedproperties can be obtained by the addition of a mixture of chlorosilanescontaining a major portion of methylchlorosilanes to a hydrolysis mediumconsisting of bis (beta-ethyloxyethyl) ether or ethylene glycol diethylether and water while maintaining the temperature of the hydrolysismedium above room temperature but not exceeding reflux temperaturesduring at least a major portion of the hydrolysis. The omission of themineral spirits or the like from the hydrolysis medium results directlyin an overall reduction in the cost of the process in that largeramounts of chlorosilanes may be hydrolyzed per given volume ofhydrolysis equipment and the polyether can be recovered and reused moreeasily than is the case when the ,alkyl chlorosilanes or aryl examplesare given:

hydrocarbon solvent is also present in the hydrolysis medium.

The chlorosilane mixtures employed in the present invention are those,containing major proportions of the methylchlorosilanes.methyltrichlorosilane forming a major proportion of themethylchlorosilane I siiane mixture. In addition to themethylchlorosilanes there may also be present various otherchlorosilanes such as ethyl, propyl. butyl, allyl, phenyl, etc.,chlorosilanes. the overall organo-to-silicon ratio of the chlorosilanemixture being at least 1 and less than about 1.5. preferably from 1.2 to1.4. In general at least 75 per cent of the chlorosilane mixtures willconsist of methylchlorosilanes.

In carrying the present invention into effect a mixture ofbis-(beta-ethoxyethyl) ether and water in an amount at least equal to,but not exceeding by more than 40 per cent, that calculated as necessaryfor conversion of the chlorosiianemixture to polysiloxanes is placed ina glass container provided with a reflux condenser. is then preferablyheated to reflux temperatures, andthe chlorosilane mixture is added tothe slowly agitated hydrolysis medium until a substantial evolution ofhydrogen chloride is obtained. Thereafter the rate of addition of thechlorosilane mixture is preferably adjusted to obtain, maximum hydrogenchloride. evolution with minimum solvent entrainment. After all of thechlorosilanes have been added the resultant mixture is heated underdistillation conditions to a temperature of about 110 degrees C. untilno more evolution of hydrogen chloride is noted.-

The temperature is then again increased sumcient to remove substantiallyall of the polyether and to leave a practically solvent-free resinsuitable for use in the various coating and other applications for whichpolysiloxane resins have previously been employed.

As will be pointed out more fully hereinafter. further cooking of theresin in the presence or absence of a solvent and under non-oxidizingconditions will produce a faster curing product.

component of the chloroheater was then turned on full and distillationbegun. 'After approximately 35 minutes and at a head temperature of95-110 degrees C. hydrogen chloride ceased coming oven: At 115 de C. theby-pass was opened and nitrogen at a pressure of 1-2 cm. mercury wasswept through the system and rapid distillation was continued forapproximately 45-minutes to obtain a nearly solvent-free resin. Theresin was then cooked with stirring at 160-170 degrees C.- for at leastonehalf hour to a 20 second cure (at 200 degrees C.).

' It was then cut with 75 g. 80 degree iwlol, stirred for 5 minutes with1-2 g. carbon black and ill tered through diatomaceous earth.

found to have parti lly But the After filtration, this resin was a slowcure (over 1 minute) and to be thermoplastic (soft at 150 degrees 0.).

resin was tougher, apparently contained longer moleculea i. e., was moreviscous. and was more compatible with other materials than a comparableresin prepared from the same mixture of chlorosilanes by the processdescribed in the above-mentioned Sauer application. The hydrogenchlorideeollected was practically pure. The

recovered distillate was found to be reusable for further hydrolysisafter adjustment for water contentJ The incorporation of small amountsof diphenyldichlorosilane into the mpthylchlorosilane mixture produces amore stable hydrolysis product which can be cooked for longer periodsafter removal of the polyether to form more viscous and more nearlycured liquid products.

In order that those skilled in the art may better understand how thepresent invention may be carried into effect, the following illustrativeclamp-controlled by-pass arrangement under the vigreaux column andcollected in a closed receiver having a draw-oil tube at the bottom. Thecharge was slowly agitated (200 R. P. M.) by means of a small T stirrerand 250 g. of a The following examples illustrate the preparation -ofmethylphenyl polysiloxanes having a phenyl-to-methyl ratio not exceeding0.25.

Example 2 A mixture of 47 g. water and 500 g. bis-(betaethoxyethyl)ether were placed in the apparatus described in Example 1. A blend of101 g. methyl trichlorosilane, 46 g. dimethyl dichlorosilane and 13 g.diphenyl dichlorosilane was added with slow stirring of the hydrolysismedium (200 R. P. M.) as follows:

Minutes Addition time until charge cleared Addition time for balance ofchlorosilane blend- 23 The charge was thenrapidly distilled to 115degrees C. head temperature, after which the bypass was opened andnitrogen swept through to complete distillation to resin base. The resinwas then cooked at 200-220 degrees C. for 2 hours to a 7 second cure(200 deg. C.) and a heavy string. After the charge temperature haddropped to 170 degrees C. the resin was cut with 75 g. petroleumspirits, stirred with 1 g. carbon methylchlorosilane mixture consistingof 80 parts methyltrichlorosilane and 20 parts dimethyldichlorosilanewere added in 13 to 14 minutes as follows: rapid stream until chargecleared, rapid drops until heat temperature steadied at 50 degrees'C.1': 5 degrees, stream adequate thereafter to maintain maximum hydrogenchloride evolution with minimum solvent entrainment. ".llhe

black (5 minutes at deg. C.) and filtered through dlatomaceous earth.YIhe resulting resin was slow curing and more thermoplastic than thatobtained with methyl chlorosilanes alone, but its solution was moreviscous.

Example 3 A mixture of 134.7 g. water and 15,000 g. bis-(beta-ethoxyethyl) ether which had been reclaimed from previoushydrolyses was placed in a hydrolyzer having a volume of 30 liters andprovided with the same type of equipment described in Example 1. Achlorosilane mixture consisting of 5737 g methyltrichlorosilane, 1388 g.dimethyldichlorosilane and 375 g. diphenyldichlorosiiane was addedrapidly to the slowly agitated charge until the liquid temperaturereached 60 degrees C.

and violent hydrogen chloride evolution had commenced. The chlorosilaneaddition. rate was then controlled to obtain maximum hydrogen chlorideevolution rate with minimum solvent entrainment. The total additionaltime was 38 minutes. A total of 355 g. of entrained liquid condensed outand was returned to the hydrolyzer. The resultant charge was distilledto 90 degrees 0. liquid temperature to remove residual hydrogen chlorideafter which the distillate was by-passed into a receiver for residualwater toa liquid temperature of 115 degrees C. Air was then blownthrough the equipment at 1 to 2 cm. Hg to a liquid temperature or 160degrees C. A total oi I 14,819 g. distillate consisting in the main ofthe polyether was collected over a period of 2 hours and 24 minutes. Theresidual resin was cut in v 900 g. petroleum spirits to form a varnish.

Preferably the hydrolysis medium is maintained at an elevatedtemperature in the neighborhood of gentle reflux temperatures during theentire time the chlorosilane mixture is being added thereto. Thispractice has been found to result in the production of hydrolyzateshaving higher cures and less subject to premature gelation than when thehydrolysis medium is at lower room temperatures during part of the time.The following example illustrates this technique as applied to achlorosilane mixture having a hydrocarbon-to-silicon ratio of 1.35 and aphenyl-to methyl ratio of 0.25.

Example 4 A' mixture of 1222 g. methyltrichlorosilane, 348 g.dimethyldichlorosilane and 430 g. diphenyldichlorosilane was dividedinto two 1000 g.-portions,

one portion was hydrolyzed without application of heat (case A) and theother was hydrolyzed hot (case B).

Case A.1000 g. of the chlorosilane blend was added to a rapidly stirredmixture of 165 g. water and 1000 g. reclaimed bis-(beta-ethoxyethyl)other over the following time-temperature cycle:

Hydro] sis Medluin Time, min.

Temp. Deg. C.

25. 68 (man). 40 (min.).

Hydrolysis Medium Temp., Dog. 0.

68 max.) heats lied. 605mm). pp

The charge was refluxed to 90 degrees C. in 17 minutes and distilled to170 degrees C. in 46 minutes without foaming. The product cured in 282seconds at 200 degrees C.

bon chlorosilanes having The upper limit of hydrolysis temperature isthe temperature of incipient appreciable solvent refluxing. In the caseof bis-(betaeethoxyethyl) ether this limit is approximately 70 degrees'0.

While the increased hydrogen chloride evolution during hot hydrolysiscauses the duration of the hydrolysis period to be increased; thesubsequent refluxing period ismaterially decreased. Thus the overalltime consumption is decreased slightly during the critical hydrolysisand refluxing periods when considerable amounts or hydrogen chloride arepresent in the charge.

What I claim as new and desire to secure by Letters Patent 01'' theUnited States is: g

1. The processof making resinous polysiloxanes which comprises adding amixture of hydrocara hydrocarbon-to-silicon ratio greater than 1 andless than about 1.5 and containing a major portion ofmethyltrichlorosilane to a hydrolysis medium consisting of water and anether solvent selected from the class consisting of bis(beta-ethoxyethyl) ether and ethylene glycol diethyl ether at atemperature above room temperature but not exceeding reflux temperaturesduring at least a major portion of the hydrolysis, the amount of waterpresent in said medium being between 1 and 1.4 times the amountcalculated as necessary to convert the chlorosilanes to thecorresponding polysiloxanes.

2. The process of making resinous polysiloxanes which comprises adding amixture of hydrocarbon chlorosilanes having a hydrocarbon-to-siliconratio greater than 1 and less than 1.5 and containing a major portion ofmethyltrichlorosilane to a hydrolysis medium consisting of water and apolyether solvent selected from the class consisting ofbis(beta-ethoxyethyl) ether and ethylene gylcol diethyl ether at atemperature above room temperature but not exceeding reflux temperaturesduring at least a major portion of the hydrolysis, the amount of waterpresent in said medium being between 1 and 1.4 times the amountcalculated as necessary to convert the chlorosilanes to thecorresponding polysiloxanes and heating the resultant products totemperature suflicient to remove substantially all of the polyethersolvent.

3. The process 01' making resinous pohrsiloxanes which comprises addinga mi ture of methylchlorosilanes having a meths l-to-silicon ratiogreater than 1 and less than 1.5 and containing a major portion ofmethyltrichlorosilane to a hydrolysis medium consisting of water and anether solvent selected from the class consisting of bis(beta-ethoxyethyl) ether and ethylene glycol diethyl ether at atemperature above room tem-- perature but not exceeding refluxtemperatures during at least a major portion of the hydrolysis, theamount of water present in said medium being between 1 and 1.4 times theamount calculated as necessary to convert the chlorosilanes to thecorresponding polysiloxanes.

4. The process of making resinous polysiloxanes which comprises addin amixture of methylchlorosilanes having a methyl-to-silicon ratio greaterthan 1 and less than 1.5 and containing a major portion ofmethyltrichlorosilane to a hydrolysis medium consisting of water and anether solvent selected, from the class consisting of his(beta-ethoxyethyl) ether and ethylene glycol diethyl ether at atemperature above room temperature but not exceeding reflux temperaturesduring at least a major portion of the hydrolysis, the amount of waterpresent in said medium being between 1 and 1.4 times the 'fl'nountcalculated as necessary to convert the chlorosllanes to thecorresponding polyelloxanea v UNITED- sTAm S Q and heating the resultantproducts to tempere- Number Name a ture sufllcient to removesubstantially all of the 2,258,218 Rochow 0 1;, 7, 194 1 ether solvent.5 2,383,827 sprung Au 33 945 W1); DOYLE 2,398,672. Bauer Apr. 16, 1948REFERENCES CITED I Carbide-and Carbon Chemlcnls 001-9.: 87n- Thefollowing references are of record in the '1 thetlc Organic (Imemmam,10th edltlon,'194th file or thlspatent: v pace 2.

